Java.Servlet.What is a “servlet container”?

A servlet container (also known as a servlet engine) is a part of a web server or application server that manages and executes Java servlets.

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🔧 In simple terms:

A servlet container is the runtime environment for servlets — it:

• Loads servlet classes
• Manages their lifecycle (init, service, destroy)
• Handles HTTP requests/responses
• Manages threading, resource pooling, session tracking, etc.

🧠 Think of it like:

🧊 JVM runs Java classes
🧱 Servlet container runs servlet classes inside a web app

💼 Common Servlet Containers

Servlet Container	Description
Apache Tomcat	Most popular standalone servlet container
Jetty	Lightweight, embeddable container
GlassFish	Full Java EE server (includes servlet engine)
WildFly (JBoss)	Java EE server (servlets + more)
Undertow	Lightweight, async servlet engine (used by WildFly)

🔄 Servlet Lifecycle (Managed by Container)

1. Class loading ➜
2. init()        ➜
3. service()     ➜ (runs on each request)
4. destroy()

The container ensures:

• One servlet class instance (singleton)
• Multiple threads for concurrent requests
• Clean up after lifecycle ends

📦 Example in Tomcat:

• You deploy a .war (Web Archive)
• Tomcat loads your servlet and maps it to a URL like /login
• When a request hits /login, Tomcat passes it to your servlet’s doGet() or doPost()

🚀 Features a servlet container provides:

• HTTP request/response handling
• URL-to-servlet mapping
• Session management
• Security (authentication, authorization)
• Multithreading
• Resource management (connection pools, caching)